Analysis of the respiratory syncytial virus (RSV) mRNAs by cDNA cloning, sequencing and related techniques has identified ten different mRNAs, and to date a single encoded polypeptide has been identified for each. We are interested in (i) continuing the analysis of the viral mRNAs and their translational open reading frames (ORFs) to detect possible additional mRNAs and polypeptides and to learn more about the details of RSV gene expression, (ii defining the extent of sequence diversity among RSV isolates, and (iii) analyzing the individual RSV proteins to determine their intracellular and virion locations and their functions. We have continued the analysis of the 1A protein (whose name has been changed to SH [small hydrophobic] to be consistent with the nomenclature for simian virus 5 and mumps virus). The SH protein was shown to be an integral membrane protein that is processed by a complex intracellular pathway that results in two nonglycosylated and two glycosylated species. The processing pathway and structural differences between the different forms have been shown to be conserved between the two RSV antigenic subgroups. Experiments are continuing to determine the membrane orientation, site of glycosylation, and the oligomeric status of the different forms of the SH protein. In other work, a complete nucleotide sequence was determined for the 22K gene of strain 18537. Comparison with the previously-determined strain A2 sequence revealed a high level (92%) of amino acid conservation for the 22K (M2) protein and identified a second, conserved ORF whose protein product remains to be identified. The high level of conservation of the 22K protein is of significance because it has been shown to be the major target antigen for RSV-specific cytotoxic T cells from infected mice (accompanying report).